PROJECT SUMMARY The Surgeon General's 2012 report provided data that the initiation of cigarette smoking begins before adulthood. Considering the new and emerging tobacco products available, estimating the age and onset of initiation, changing patterns of tobacco use and correlates of tobacco use among U.S. youth and young adults is paramount to informing contemporary tobacco regulatory science. We will directly inform the Food and Drug Administration (FDA) authority on tobacco regulation about all tobacco products to protect the public?s health. This project directly address the FDA's research priority areas that focus on understanding the knowledge, attitudes, and behaviors that contribute to tobacco product (TP) initiation, age of TP initiation, and factors associated with age of initiation. Our study involves a prospective secondary analysis of the first three waves of the Population Assessment of Tobacco and Health (PATH) study among U.S. youth (12-17 years old) and young adults (18-24 years old) who reported never use at baseline. Six TPs will be considered: cigarettes, e- cigarettes, cigars (i.e. traditional cigars, cigarillo, filtered cigars), hookah; smokeless tobacco, and any of these TPs. Seven outcomes are considered for each TP: age to first report ever or past 30-day use, age to become susceptible to use, age to be an established user (i.e. ever use fairly regularly), age to first report dual/poly TP use, age to first use flavored TP, and age of ever combustible use. There is a gap in the knowledge related to the age of first reporting of each one of the seven outcomes prospectively and with contemporary data. This project has three aims. Aim 1: Among youth ages 12-17 years old who are never users of TPs at wave 1, to estimate prospectively their age of initiation of TPs and to identify the risk factors associated with the age of initiation of cigarettes and each one of the NCTPs: e-cigarettes, cigars, hookah, and smokeless tobacco. Aim 2: same as aim 1 but among young adults ages 18-24 years old who are never users of TPs at wave 1. Aim 3: Among youth and young adults ages 12-24 who are never users of TPs at wave 1, to identify the trajectories and transitions in the onset of TPs across time, from wave 1 to waves 2 and 3, and to identify the risk factors associated with these trajectories and transitions. We plan to explore socio-demographic, interpersonal, intrapersonal, social, and environmental factors potentially associated with the age of initiation of the different TPs. Consistent with research priorities FDA has set forth, this project focuses on our understanding of the knowledge and behaviors to best predict age of initiation. Few studies can test hypotheses with longitudinal data that span youth and young adults. This project strengthens the evidence for tobacco regulatory science by expanding the evidence regarding emerging tobacco products, using a national longitudinal study, and taking advantage of contemporary data that reflects the evolving tobacco product landscape. This project addresses RFA-OD-18-002.